In the current state of the automobile industry, the application of ultrahigh strength steel sheets is increasing in order to cope with the requirements of safety and lightness. However, it is difficult to use ultrahigh strength steel sheets to produce automobile parts having complicated shapes because they have low formability. Thus the demand for quenchable steel sheets ensuring high strength by heating, hot pressing and then quenching them.
This section is to provide general background information, and does not constitute an admission of prior art.